The present invention relates to an electrophotographic photoreceptor which contains a novel bis-azo compound.
Hitherto, for electrophotographic photoreceptors, inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, and silicon have been known, widely studied and put to practical use. These inorganic materials have many merits, but at the same time, have also various defects. For example, selenium has the difficulty in production conditions and is readily crystallized by heat or mechanical shock. Cadmium sulfide and zinc oxide have difficulties in moisture resistance and endurance. Insufficient chargeability and difficulty in production have been pointed out for silicon. Furthermore, selenium and cadmium sulfide have the problems of toxicity.
On the other hand, organic photoconductive materials have advantages in superior film-forming properties and flexibility, lighter weight, higher transparency and easier design of photoreceptors using proper sensitizing methods.
Fundamental properties generally required for electrophotographic photoreceptors include (1) high chargeability when exposed to corona discharge in the darkness, (2) less leakage, in the dark, of the charge obtained (dark decay), (3) rapid release of the charge when exposed to light (light decay), and (4) little residual charge after exposure to light.
Many studies have been made on photoconductive polymers such as polyvinylcarbazole to be used as organic photoconductive materials. However, these materials are not satisfactory in film-forming properties, flexibility and adhesiveness and besides, cannot be said to fully meet the above-mentioned fundamental requirements for photoreceptors.
On the other hand, photoreceptors superior in film properties and mechanical strength such as adhesiveness or flexibility can be obtained with organic low molecular photoconductive compounds if binders for making the photoreceptors are selected, but it has been difficult to find compounds suitable to maintain the characteristic of high sensitivity.
Organic photoreceptors of high sensitivity have been developed by carrying carrier generating function and carrier transporting function on different materials to improve the above-mentioned problems. The feature of these photoreceptors called double-layered photoconductive structures is that materials suitable for respective functions can be selected from a wide variety of materials and photoreceptors having optional performances can be easily produced. Thus, various researches have been made thereon.
As mentioned above, various improvements have been made in production of electrophotographic photoreceptors, but those which fully satisfy the above-mentioned fundamental properties and high endurance required for photoreceptors have not yet been obtained.